1. Field of Invention
The present invention concerns a method and equipment for distribution of two fluids into and out of channels of a multi-channel monolithic structure (monolith) where the channel openings are spread over an entire cross-sectional area of said structure.
The present invention is applicable in processes for mass and/or heat transfer between two fluids.
2. Description of the Related Art
The industrial use of monoliths is limited mainly to applications in which only one fluid flows through all the channels at the same time.
In literature identified below, a number of processes or applications are described in which monoliths can be used to improve transfer heat and/or mass between two different fluid flows. Small-scale experimental tests have also been carried out with such processes. An example of this is production of synthesis gas (CO and H2). Synthesis gas is normally produced using steam methane reformation. This is an endothermic reaction in which methane and steam react to form synthesis gas. Such a process can be carried out in a monolith in which an exothermic reaction in adjacent channels supplies heat to the steam methane reformation.
Although it has been shown that it will be advantageous to use monoliths for mass and/or heat exchange between two fluids in a number of applications, industrial use of monoliths for such applications is not very widespread. One of the most important points of complaint or reasons why monoliths are not used in this area is that the prior art technology for feeding and distributing the two fluids into and out of the monolith's separate channels is complicated and not very suitable for scaling up (i.e. interconnection of several monolith units), particularly when the large number of channels in a monolith are taken into consideration.
German patent DE 196 53 989 describes a device and a method for feeding two fluids into the monolith's channels through feed pipes. These feed pipes or tubes feed the two fluids into the monolith's respective channels from the plenum chambers of the respective fluids. The plenum chambers are mounted together in such a way that tubes from the outer chamber must be fed through the inner chamber and subsequently into the monolith's channels. Each individual tube must be sealed in order to prevent leakage from the channels of the monolith and from lead-throughs in the walls of the plenum chambers. When heated, the monolith, plenum walls, pipes and sealing material will expand, and, when cooled, they will contract. This increases the likelihood of crack formation and undesired leakage with mixture of the two fluids as a consequence. This likelihood will increase with the number of pipe lead-throughs.
In DE 196 53 989, the inlet and outlet zones with the sealed pipes are cooled so that a low-temperature, flexible sealing material can be used and the risk of crack formation and leakage can be reduced. A cooling system will naturally make the monolithic structure more expensive and more complicated, particularly for applications on a large scale in which the monolith consists of many thousand channels and in which it is also necessary to use many monolithic structures in series and/or in parallel to achieve a sufficient surface area.
U.S. Pat. No. 4,271,110 describes another method for feeding two fluids in and out. This method has the advantage that pipe in-feeds from the plenum chamber to the channels of the respective fluids in the monolithic structure can be dispensed with completely. This is achieved by cutting parallel gaps down the ends of the monolith. These cuts or gaps lead into or out of the channels for one of the fluids. The gaps cut then correspond to a plenum chamber for the row of channels that the gap cuts through. By sealing the gap's opening that faces out towards the end of the monolith, openings are created in the sidewall of the monolith where one of the fluids can enter or leave. The other fluid will then enter or leave at the short end of the monolith in the remaining open channels. A major disadvantage of this method, apart from the necessary processing (cutting and sealing) of the monolithic structure itself, is that only half of the available area for mass and/or heat exchange can be utilized. For example, square channels for one fluid and the other fluid will have to lie in connected rows so that the channel structure for the two fluids corresponds to a plate heat exchanger. If the channels for the two fluids were distributed as in a chessboard pattern, where the black fields correspond to channels for one fluid and the white fields correspond to channels for the other fluid, the maximum utilization of the area could be achieved because, in such a fluid distribution pattern, all the walls of the channels for one fluid would be joint or shared walls with those of the other fluid. With fluid channels for the same fluid in a row as in U.S. Pat. No. 4,271,110, roughly only half of the channels' walls will be in contact with those of the other fluid.